1. Field of the Invention
The present invention relates generally to radiation applicators for use in the treatment of cancerous tissue and, more particularly, to such an applicator having a measuring device to indicate the distance between the radiation sources and healthy tissues.
2. Description of the Prior Art
One of the most common sites of cancer in women is the uterine cervix, and it is customary to treat the cancer by irradiation with radioactive sources. A radioactive source applicator to which the present invention typically relates is the Henschke afterloading applicator described below. Typical patents directed to radioactive source applicators include:
U.S. Pat. No. 3,789,829
U.S. Pat. No. 3,323,511
U.S. Pat. No. 3,060,924
U.S. Pat. No. 2,888,917
U.S. Pat. No. 2,544,939.
The major problem with such devices is that they place the source of radioactivity so close to the rectum that it makes the rectal dose of radiation the limiting factor in the internal treatment. Thus, the rectal dose must be measured accurately to avoid over-irradiating the rectal area and harming healthy tissues in the process of treating diseased tissues.
To determine the rectal dose in most patients, the following procedure is followed. The radioactive source applicator is inserted and positioned in the vagina. A material not penetrated by X-rays is injected in the rectum, and an X-ray is then taken. The cervix-rectum distance is determined from the X-ray. This information along with the radioactive strength and position of each of the sources is fed into a computer. The computer determines the radiation levels in a series of what are called isodose curves. Isodose curves give a somewhat 3-dimensional view of the fall off of the radiation level with distance from the radioactive sources. The doctors can site the location of the rectum on this set of curves and thus estimate the rectal dose.
Among the problems associated with the isodose curve method are that the X-ray does not give an accurate measurement of the cervix-rectum distance measurement while it exposes the patient to additional radiation and requires computer facilities which are not always readily available.
For more accurate measurements there are several devices for determining the radiation level exactly. The first of these is an ion chamber which produces small pulses of current when the X-rays ionize the air inside. The pulses are so small they require a special preamplifier and counter. The second method used involves a scintillation detector, a material that takes in X-rays and turns out small amounts of visible light. The visible light is then light piped to a photo multiplier and then to a special counter. Both of these methods are expensive and somewhat complex and therefore do not afford simplicity and economy.
Because cervical cancer is a disease found, to a large degree, in underdeveloped countries, and in the lower economic communities of this country, any solution to this problem must be applicable to such areas where large and expensive facilities generally do not exist.